For me it's the other way around. I was folding and overclocking at the same time when I stumbled over this behavior. I paused the folding process and then the mem offset stuck.

This just started happening to me after installing a second 980 Ti in SLI. Funny thing is, only one of the cards has this problem. I noticed it running Fire Strike Ultra. One card resets its memory clock offset back to zero as soon as I start the benchmark.
 
(hah - I see this thread is a year old... don't suppose anyone's found a solution?)